Analysis of Post-acidification Property of Lactobacillus bulgaricus Based on Sucrose Metabolism Pathway
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Abstract:
Weak post-acidification ability is an important characteristic of lactic acid bacteria when being used as a starter culture. In order to study the role of Lactobacillus bulgaricus sucrose metabolic pathway on post-acidification of fermented milk, in this study, the post acidification performances of five Lactobacillus bulgaricus strains was compared, the growth status, sugar metabolism and acid production capacity of Lactobacillus bulgaricus were analyzed, the differential expression of genes related to sucrose metabolism and acid production and the activities of key enzymes were investigated, and the growth of Lactobacillus bulgaricus before and after the exogenous addition of key enzymes for sucrose metabolism, were studied. The results showed that Lb. 1 had the weakest post-acidification ability and grew slowly in the medium with sucrose as the carbon source. KLDS 1.0207 had the strongest post-acidification ability. After fermentation for 24 h, the sucrose conversion rates were 5.85% and 85.39%, respectively, and the lactic acid contents were 1.13 g/L and 11.81 g/L, respectively, for these two strains. The expression levels of sacA, pgi, gap, pgk and ldh in the sucrose metabolism pathway of KLDS 1.0207 were extremely significantly higher than those for Lb.1 when MRS containing disaccharide (lactose:sucrose=1:1.5) was used as the growth medium (P<0.01), with the activity of sucrose enzyme of KLDS 1.0207 being significantly higher (reaching 1.31 U/mg) than that of Lb. 1 (P<0.05). The OD600 nm increased by 5 times after sucrase was supplemented into the sucrose medium of Lb. 1. Therefore, the activity of sucrase is crucial for the sucrose metabolism in Lactobacillus bulgaricus. The downregulation of the expression of sacA gene encoding sucrase significantly weakened the activity of sucrase, and the post-acidification ability of the strain decreased significantly.
